California Quadrajet
Thread Starter
Instructor
Joined: May 2006
Posts: 223
Likes: 1
From: Kennesaw GA
California Quadrajet
Ok, here's another post on our favorite subject, the QuadraJet.
I've just finished a complete rebuild of the rear suspension, drivetrain, brakes and a new fuel tank on my '69. Now it's off the jack-stands and trying to get it running right. Currently it is WAY rich, and the idle mixtures screws don't change anything. I've been all over Lars' document on the Q-Jet (love it by the way) and after decoding the casting number on the 'Jet, (70 40 5 0 9) I see that it is a California/High altitude model from 1970.
Does anyone know anything about the differences in this carb with the other 49 state models? I would imagine that stock jetting would be different, but I'm not sure.
Anyway, I'm thinking the primary/power jets are not functioning properly, I don't think they are being pulled down by vacuum at idle, causing it to be way rich.
Here's a pic of the rods,are there supposed to be any o rings or gaskets in the grooves? I don't see where the vacuum seal would be on this.
Thanks for any insight.
I've just finished a complete rebuild of the rear suspension, drivetrain, brakes and a new fuel tank on my '69. Now it's off the jack-stands and trying to get it running right. Currently it is WAY rich, and the idle mixtures screws don't change anything. I've been all over Lars' document on the Q-Jet (love it by the way) and after decoding the casting number on the 'Jet, (70 40 5 0 9) I see that it is a California/High altitude model from 1970.
Does anyone know anything about the differences in this carb with the other 49 state models? I would imagine that stock jetting would be different, but I'm not sure.
Anyway, I'm thinking the primary/power jets are not functioning properly, I don't think they are being pulled down by vacuum at idle, causing it to be way rich.
Here's a pic of the rods,are there supposed to be any o rings or gaskets in the grooves? I don't see where the vacuum seal would be on this.
Thanks for any insight.
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
There are no gaskets or O rings on the power piston. Clean it with carburetor cleaner and use some Scochbrite on it. Make sure its bore is clean. Be careful with these parts don't scratch or score them. Clean them enough to have the piston move in the bore without binding, no more.
While you're there record the jet/rod numbers.
Is this the original carburetor? Has someone else had control of this carburetor? If so it could have any combination in it.
BigBlockk
Later.....
While you're there record the jet/rod numbers.
Is this the original carburetor? Has someone else had control of this carburetor? If so it could have any combination in it.
BigBlockk
Later.....
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
the power piston looks discolored like it has been hot or exposed to exhaust gas. is the carburetor being used on a 1968 or 1969 intake manifold? if so the stainless steel plate that goes between the base gasket and the carburetor and keeps the exhaust that comes up to the carburetor yet out of the carburetor may be missing.
this would cause exhaust instead of vacuum to be present at the point where the carburetor gets its vacuum for the power piston.
i hope this helps henry @ oles carb
this would cause exhaust instead of vacuum to be present at the point where the carburetor gets its vacuum for the power piston.
i hope this helps henry @ oles carb
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
There's a spring that pushes the power piston up when the vacuum signal drops such as WOT. That spring needs to match your engine. If it's too stiff and/or your vacuum is low (what cam are you running?) it could create some "too rich" problems by keeping the power piston "up" and the power circuit "on" more than it should be. There are spring kits that allow you to fine tune the power circuit.
olescarb,..agree-squared! I hate those intakes with the 'heat trough' on front of the primaries. What a crummy idea that was.
olescarb,..agree-squared! I hate those intakes with the 'heat trough' on front of the primaries. What a crummy idea that was.
Thread Starter
Instructor
Joined: May 2006
Posts: 223
Likes: 1
From: Kennesaw GA
Thanks for the tips guys. I haven't run the numbers on the manifold yet, but it is an aluminum GM one. I'll post the numbers and pictures of the manifold and see what I'm missing for under the carb. When I took the carb off for cleaning, I don't recall a piece of stainless underneath the carb... is it like a gasket or a block off plate?
I'm trying to control my 5 mo old son right now, so I'll post pics in a little bit.
BTW, this is a '69 427/390
Thanks!
I'm trying to control my 5 mo old son right now, so I'll post pics in a little bit.
BTW, this is a '69 427/390
Thanks!
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
It looks like a gasket but is made of stainless steel about 050" thick maybe less. If this is an L-36 manifold it has the exhaust gas crossover. These were used because there was no hot air induction to the carburetor and the aluminum manifold sheds heat so quickly carburetor icing could be a problem.
BigBlockk
Later.....
BigBlockk
Later.....
Thread Starter
Instructor
Joined: May 2006
Posts: 223
Likes: 1
From: Kennesaw GA
So was the standard L36 intake aluminum? Also, mine doesn't have a heat riser valve, just a spacer. I thought someone had replaced it somewhere down the line, but maybe this is stock?
Thanks again!
Thanks again!
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Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Did you ever have this carb running correctly on the manifold that it's on now?
If the idle screws are not changing anything then I would guess the piston isnt seated all the way at idle.
Easy way to test this is.. at idle take a long thin screwdriver and insert in the tube closest to the front of the carb.. you will feel the top of the piston.. you should not be able to push it down... the vacuum should be holding it down.
Turn the engine off and and try it again, it should move freely as there is now no vacuum
If the idle screws are not changing anything then I would guess the piston isnt seated all the way at idle.
Easy way to test this is.. at idle take a long thin screwdriver and insert in the tube closest to the front of the carb.. you will feel the top of the piston.. you should not be able to push it down... the vacuum should be holding it down.
Turn the engine off and and try it again, it should move freely as there is now no vacuum
Thread Starter
Instructor
Joined: May 2006
Posts: 223
Likes: 1
From: Kennesaw GA
I have a feeling that when I took off the old carb gasket, the heat shield was stuck to it, and I threw it out not knowing any better. I've got one on order from the local parts house, and then I can check to see what is happening. I know the car ran fine with the current setup, as my Mom drove it for the last time in 1985, since then it just sat.
So will that heat shield missing really cause the rich condition, or should I be looking further into the carb? I've gone over the power piston and everything looks fine.
Thanks again!
So will that heat shield missing really cause the rich condition, or should I be looking further into the carb? I've gone over the power piston and everything looks fine.
Thanks again!
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
the heat shield missing would also cause exhaust gas to go directly into the intake system, so as long as the power piston moves free you should be ok. if you ever have the intake off, blocking the passages that go up to the carb by tapping those passages to 1/4" pipe and installing allen plugs to block that part of the exhaust flow thru the intake manifold would be a good idea. the reason exhaust was supplied to the carb base was to heat the carb and prevent iceing the carb. but with todays reformulated gasoline heat is the enemy of a carburetor.
good luck and i am happy you found the problem
henry @ oles carb
good luck and i am happy you found the problem
henry @ oles carb
Thread Starter
Instructor
Joined: May 2006
Posts: 223
Likes: 1
From: Kennesaw GA
Ok, so the heat shield missing will not cause the rich problem. I do like the idea of plugging off the exhaust holes in the manifold... I bet I can do that without waiting for parts to arrive. As for the carb, I'll clean everything up again and see what I get.
Thanks for all the help!
Thanks for all the help!
